Project Summary/Abstract.! This R13 application requests funds to support the XXIVth North American Testis Workshop, to be held April 19 - April 22, 2017 in Miami, Florida. The requested funds are intended to help defray travel costs for 10 young investigators, selected for short talks from submitted abstracts, and housing costs for 20 invited speakers. Since 1972, the North American Testis Workshop has been the premiere international forum for basic and clinician-scientists to present and discuss their recent findings on testis regulation and function. The main goals for the Workshop are to: 1) facilitate solutions for the high incidence of male infertility and the need for a safe, reversible male contraceptive and 2) foster development of the field's future leaders, with emphasis on trainees, women and underrepresented minorities.! The Workshop's theme is ?From Testis Differentiation to Sperm Production?. The program includes four major lectures (the keynote address and three benchmark lectures) and 16 invited talks that are grouped into six sessions as follows: Germline Establishment & Homeostasis (Session I), Germ cell Differentiation and Maintenance: Role of RNA & RBPs (Session II), Testis Development & Differentiation (Session III), Transcriptional & Endocrine Regulation in the Testis (Session IV), Sperm Development & Maturation (Session V), and Genetics & Epigenetics of Male Reproduction (Session VI). After invited talks, sessions will end with short talks selected from abstracts submitted by young investigators (trainees and Assistant Professors in rank for no more than 2 years). Two poster sessions, with all posters displayed throughout the meeting, are also planned. The meeting will begin with the keynote address by Dr. Dirk de Rooij, from Utrecht University, The Netherlands. Dr. de Rooij is a longstanding leader in the field of testis biology who has contributed extensively to our understanding of the testis, by documenting fundamental characteristics of different testicular cell types and their relation to spermatogenesis and male fertility. His presentation will offer new insights on spermatogonial renewal and differentiation in humans and non-primates and provide a strong foundation for many subsequent presentations. Dr. Haifan Lin, from Yale University, will give the first benchmark lecture. Dr. Lin is internationally recognized for his research on germline self-renewal and development and the Piwi-piRNA pathway and its role in epigenetic programming and posttranscriptional regulation. His presentation will provide a strong foundation for Sessions I & II. Dr. John Aitken, from the University of Newcastle, Australia, will present the second benchmark lecture. Dr. Aitken is a leading authority on male infertility and his lecture is relevant to presentations throughout the meeting but mostly to those in Sessions V and VI. Dr. Oliver Rando, from the University of Massachusetts, will give the third benchmark lecturer. Dr. Rando is well known for his research on chromatin and epigenetic inheritance and his talk on the sperm epigenome, paternal inheritance and influences from diet and the environment merges nicely with topics in Sessions V and VI.